1. Field of the Invention
The present invention relates to a battery pack provided with a memory and a secondary battery, a charging device for charging the battery pack, and an electronic device using the battery pack as a power supply.
2. Description of the Related Art
Conventionally, some types of battery packs for use in an electronic device are provided with a nonvolatile memory for storing a nominal charge capacity value and a remaining charge capacity value.
Further, there has been proposed a charging device for charging a battery pack of the above-mentioned type, in which the remaining charge capacity value is calculated based on a result of electric current integration and an initial remaining charge capacity value and a nominal remaining charge capacity value stored in a nonvolatile memory, and the initial remaining charge capacity value is rewritten into the calculated present remaining charge capacity value (see e.g. Japanese Patent Laid-Open Publication No. H06-310179).
Furthermore, an electronic device on which such a battery pack is mounted is configured to be capable of calculating a battery available time period from the present remaining charge capacity value and a load current.
In techniques typified by the above-mentioned prior art, however, since the remaining charge capacity value is stored in the nonvolatile memory, the calculation of the integral of charging current and that of load current is indispensable. With this configuration, it is impossible to accurately measure an electric current in the case of an electronic load where rush current frequently occurs, which is a factor causing an accuracy error in the measurement of the remaining charge capacity. Further, it is required to provide a device for measuring a current value on a power supply line, which causes a drop in voltage, thereby impeding improvement of power efficiency.